The European GaN Workshop held in Warsaw, Poland was the third in a row starting 1996 at Rigi, Switzerland and followed by Valbonne, France (1997). Since EGW-1 the numbers of attendees and contributed papers are steadily increasing, culminating into a total of 150 participants for EGW-3 (POL 35, GER 22, UK 13, USA 13, F 13, R 12, etc.) Therefore, one of the many challenges encountered by the Organizers was to keep the character of a workshop even with such a high number of attendees. The Organizers from Unipress, High Pressure Research Center of Polish Academy of Sciences solved this problem with sovereignty. They relied on very short talks (7 minutes), which is already tradition at EGW and two poster sessions, being a novelty to the workshop. The European GaN community owes a honest appreciation to the successful organizers as well as to the strict chairmen and the very responsible speakers. They all kept the workshop within its schedule and helped to make it a success.
EGW-3 can be summarized by the search for suitable substrates for GaN technology since high quality high end devices obviously require substrates superior to sapphire or SiC. GaN single bulk crystals, free standing GaN layers, ELOG quasi-substrates or thick GaN layers by HVPE or MOVPE will play a significant role and have been investigated extensively. Each approach having its particular advantages and disadvantages. Furthermore, piezoelectric effects and their impact on devices and the Ga- or N-termination of the various surface have been hot and controversial topics.
EGW-3 started with a brief retrospect on GaN history by the scientist who led the field for many years, J.Pankove. Afterwards, the workshop had the honor to have today's leading scientist, S.Nakamura, opening the technical sessions with his talk on GaN based laser diodes. He reported a measured lifetime > 6,000 hours, max. optical power up to 420 mW and a threshold current density of 1.2 kA/cm2 all for 300 K, cw operation. He also sets pace with the most obvious trend at EGW-3, the improvement of devices by an enhanced crystalline quality using either bulk GaN substrates or lateral overgrowth by MOVPE or HVPE. Nakamura reported the first GaN laser grown on free standing GaN films. 200 µm thick GaN has been deposited on sapphire substrates using epitaxial layer overgrowth (ELOG), subsequently the sapphire was removed. Thereby, cleaved facets are easily to obtain and the thermal resistance of the device is reduced by a factor of 2. However, some laser characteristics are yet still inferior to data obtained with conventional ELOG lasers.
Beside GaN single bulk crystals, a field still leaded by Unipress, quasi-substrates made by HVPE and/or ELOG gain increasing importance for GaN technology. The enormous potential of those techniques can be estimated by the excellent results presented by B.Beaumont, who presented very narrow PL linewidths using MOVPE ELOG and Mg doping.
Optical devices presented at EGW-3 included laser, LEDs from 370 - 595 nm,
LEDs on GaN substrates, improved LED reliability and the understanding of the
light emitting mechanisms. Additionally, photodetectors with excellent device
characteristics have been reported using hetero- and homoepitaxial layers.
An overview about electronic devices and their applications was given by Lester Eastman in an invited talk. Further contributions on FETs reported dopant free transistors as well as high temperature performance of modulation-doped (MOD)FETs. Operation of HFETs up to 750°C reported by I.Daumiller are as impressive as promising for electronic applications.
Special sessions on crystal growth by MBE and VPE have been opened with invited overviews presented by T.Foxon and V.Dmitriev, respectively.
With MBE either GaN substrates or quasi-substrates (e.g. MOVPE or HVPE grown
templates) gain increasing importance, since obviously they can significantly
improve the quality of the subsequent MBE layers. Contributions on VPE were
mainly focused on the preparation and improvement of such quasi-substrates by
thick layers or ELOG.
Dopants and Defects were the topics of another session opened by an invited
talk on Positron annihilation studies by P.Hautojärvi. By this method,
VGa have been identified to be responsible for the yellow
luminescence. Other contributions dealt theoretically and experimentally with
shallow acceptors and donors.
The session on properties and characterization had an invited talk by
G.Dollinger on elastic recoil detection (ERD) an unusual but yet powerful
technique to determine composition and impurities. Other talks dealt with high
quality materials and phase separation of InGaN and AlGaN. Physical properties
of GaN based semiconductors were addressed in another session opened with an
invited talk by R.Stepniewski. PL and Raman scattering are still the typically
used optical techniques to access the physical properties of III-Nitride
semiconductors.
Wednesday morning was devoted to microstructural properties. A.Hangleiter presented the current knowledge on piezoelectric effects in GaN based structures in an invited talk. The resulting fields are of significant importance for FETs and QW devices such as LEDs and LDs. J.L.Rouviere subsumed in his invited talk information gather by electron microscopy on the surface termination and heterostructures. M.Leszczynski summarized the achievements in homoepitaxial growth on GaN single bulk substrates at several European laboratories in his talk. The last session started with an invited talk by R.M.Feenstra on Ga- and N-terminated surfaces in MBE. Wet chemical etching, surface termination and ad layers were addressed by experimental and theoretical techniques in this final session.
The two poster sessions were very well attended. 32 posters presented in two sessions covered all fields of III-Nitride research from theoretical and fundamental research to devices. The Rump Session organized by E.Weber was on GaN based devices. Within the rump session, the panel members (which were with one exception from the USA and Japan) encouraged the attendees to contribute to the improvement of GaN device by direct contributions or by fundamental research. Again, the rump session concluded explicitly the importance of improved substrates for GaN technology.
Beside many excellent scientific contributions, the welcome party on Sunday
night and the outstanding Conference diner which took place at Pultusk, the
former residence of an archbishop 20 km from the conference site, were
appreciated by all attendees. The attendees enjoyed the entertainment of the
local music group and the dinner and got really excited when famous colleagues
such as J.Zavada, J.L.Rouviere, etc. got hold of the microphone. After EGW-3,
almost 40 attendees followed the kind invitation by Prof. Porowski to
Celestynow and spent another wonderful day at the remote compound of Unipress
in the south of Warsaw. Everyone enjoyed a wonderful barbecue, swimming and a
spontaneous soccer match.
Two years ago, after EGW-1, this author made the point that Europe is particular strong in characterization and fundamental research but that we still have a gap with respect to device research performed in USA and Japan. Despite the increased number of contributions on device research in EGW-3, the situation was very similar to that of EGW-1. For example, only two out of the 10 invited talks dealt with devices and both speakers came from abroad; the remaining eight talks on growth, characterization, etc., were all, save one, given by European researchers.
The perfect organization of the workshop and the wonderful finale in Celestynow places a big burden on the orgainizers of the next European GaN Workshop which will be held at University of Nottingham, UK. John Orton will serve as the chairman of the workshop which presumably takes place in July 2000, since in 1999 the biannual Third International Conference on Nitride Semiconductors (ICNS'99) will be held in Europe (Montpellier, France). Everybody who watched John Orton playing soccer at Celestynow is sure that we are looking forward to a highly dynamic, enthusiastic, organized and fair event (the workshop that is!). The author was happy to be on his team!
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